1. Field of the Invention
The present invention relates to an electrostatic machine element, a light diffraction modulation element and an image display device using the same, and for example a light diffraction modulation element like a diffraction grating type light valve reflecting and diffracting light, and a two-dimensional image display device using the same.
2. Description of the Related Art
It is known a method in which luminous flux from a one-dimensional image display element is scanned by a light scanning means and the scanned flux is projected to an image forming means to form a two-dimensional image, for the purpose of improving a resolution of an image in an image forming device like a projector or a printer (U.S. Pat. No. 5,982,553). As the one-dimensional image display element, a grating light valve (GLV) developed by Silicon Light Machine Corporation in U.S.A. is known (Japanese Patent No. 3164824, U.S. Pat. No. 5,841,579).
The GLV is composed of a micro machine phase reflection type diffraction grating utilizing a diffraction phenomenon of light. The GLV has a light switching function, and electrically controls an ON/OFF control of a light to enable a digital image display.
The GLV formed as a one-dimensional array is scanned by a scanning mirror to obtain a two-dimensional image. Therefore, compared with normal two-dimensional display devices, in case of using the GLV, although the number of pixels at a vertical direction are same as that of them, since the number of pixels at a lateral direction may be at least one, the number of pixels needed for displaying a two-dimensional image is small. Further, a size of an electrode portion of the GLV called as a ribbon element is extremely small, so the GLV can display the image at a high resolution, at a high-speed switching and with a broad band width. In addition, the GLV can be operated at a low application voltage, so the GLV has been expected to realize a display device of extremely miniaturization.
The two-dimensional image display device using such the one-dimensional image display element GLV enable an extremely smooth and a natural image expression compared with the normal two-dimensional image display devices, for example a projection type display device using a liquid crystal panel, because boundaries between pixels does not exist in the GLV. Moreover, lasers of red, green and blue as the three primary colors are used as light sources and these lights are mixed to achieve a superior display performance enabling an image expression of extremely broad and natural color reproduction range, which is not achieved by a prior art.
A ribbon element of the GLV is a micro machine driven by electrostatic force and displaced or deformed, and one of fine electrostatic machine elements.
FIGS. 10(a) and (b) are views explaining a structure and an operation of an electrostatic machine element in GLV.
FIG. 10(a) is a schematic cross-section view showing a structure of an electrostatic machine element as the related art. As shown in FIG. 10(a), an electrostatic machine element 100 is formed by a lower electrode 102 as a lower structure composed of a polysilicon on a substrate 101 of silicon or a glass, and a dielectric film 103 for protecting the lower electrode 102 and composed of silicon oxide (SiO2) on the lower electrode 102. Further, the electrostatic machine element 100 is also formed by an upper electrode 105 as an upper structure composed of for example aluminum on a dielectric film 104 composed of silicon nitride (SiN). The dielectric film 104 and the upper electrode 105 compose a single ribbon element. In the state shown in FIG. 10(a), a voltage is not applied between the upper electrode 105 and the lower electrode 102 and the electrostatic machine element 100 is in an OFF state.
FIG. 10(b) is a schematic cross-section view showing a structure of an electrostatic machine element. As shown in FIG. 10(b), when a certain drive voltage is applied between the upper electrode 105 and the lower electrode 102, an electrostatic force (Coulomb force) is caused between the upper electrode 105 and the lower electrode 102 (It is called as an ON state). As a result, for example, the upper electrode 105 is mechanically displaced or deformed (warp) to the lower electrode 102 side. The amount of displacement or deformation (warp) (the movement amount) a1 is nm (nano meter) order and corresponds to a value of a drive voltage. When a plurality of electrostatic machine elements 100 are arranged in parallel, a reflection type diffraction grating is formed by the warp or the movement amount a1 to generate a diffraction light.
FIG. 11(a) is a cross-section view showing an electrostatic machine element at time to and FIG. 11(b) is a cross-section view showing an electrostatic machine element at time t1.
In a micro machine device for forming an opposed electrodes through a dielectric film and performing drive by an electrostatic force like the electrostatic machine element 100, as shown in FIG. 11(a) and (b), a drive voltage is applied to make the upper electrode 105 a high electric potential and the lower electrode 102 a low electric potential to be the ON state. The upper electrode 105 is displaced in a direction of the lower electrode 102 with the distance a1. However, a phenomenon has been observed that the position of the upper electrode 105 is gradually displaced in the direction of a position of the OFF state with the elapse of time.
Specifically, in FIG. 11(a), the drive voltage shown in FIG. 10(b) is applied to displace the upper electrode 105 to the lower electrode 102 side by the distance a1 at the time t1. At time t1 after the elapse of time, the upper electrode 105 is returned in a direction opposed to the lower electrode 102 side to be at a distance a2 smaller than the distance a1 compared with the distance before the drive voltage is applied.
This phenomenon is considered by which the electrostatic force between the upper electrode 105 and the lower electrode 102 is weak.
As shown in FIG. 10(a), in an atmosphere at a high vacuum, molecules existing in low density for example moisture are deposited to the dielectric films 103 and 104. As shown in FIG. 10(b) and FIG. 11(a), when the drive voltage is applied at around 20V for example between the upper electrode 105 and the lower electrode 102, since the distance between the dielectric film 103 and 104 is around 1 xcexcm, a high electric field at around 20 V/10xe2x88x924 cm=2xc3x97105 V/cm is formed between the upper electrode 105 and the lower electrode 102.
When the molecules for ionizing regularly in a normal temperature like H2O molecules adheres to the dielectric films 103 and 104 or floats between the electrodes, the molecules for ionizing regularly described above (charged particles) repeat ionization and bonding in the state of adhering to the surface or floating between the dielectric films 103 and 104 to keep equilibrium of the particles. Even if adding the high voltage described above in this state, these ionized charged particle are restrained by an adhesion force of the dielectric films 103 and 104, so that they cannot immediately apart from the dielectric films 103 and 104. Then, aparting from the dielectric films 103 and 104 with the elapse of time, as shown in FIG. 11(b), the charged particles move between the dielectric films 103 and 104 along with the direction of the electric field.
Specifically, the voltage is applied to the upper electrode 105 at a high electric potential and a low electric potential is applied to the lower electrode 102 as described above, so that a positive charge adhered to the dielectric film 104 of the upper electrode 105 moves to the dielectric film 103 of the lower electrode 102 and a negative charge adhered to the dielectric film 103 of the lower electrode 102 moves to the dielectric film 104 of the upper electrode 105.
According to a movement of electric charges between the upper electrode 105 and the lower electrode 102 described above, the upper electrode 105 and the lower electrode 102 have the respective negative charges and positive charges as a whole. Negative charges and positive charges adhered at the surfaces of the dielectric films 103 and 104 brings about an electric field in a direction opposed to the electric field formed by the drive voltage at a space between the upper electrode 105 and the lower electrode 102. As a result, so-called an electrostatic shielded effect that the available electric field between the upper electrode 105 and the lower electrode 102 is getting weak takes place. Due to the shielded effect, an electrostatic force between the upper electrode 105 and the lower electrode 102 is getting weak and does not enable to keep the upper electrode 105 at the position of the distance a1, as a result the upper electrode 105 is gradually returning to the base position. The electrostatic shielded effect is called a charging phenomenon (charging).
FIG. 12 is a graph showing a change of the movement amount of the upper electrode 105 by the charging phenomenon. In FIG. 12, the x-axis shows a relative value of a drive voltage, the y-axis shows the movement amount of the upper electrode 105 and a unit is xcexcm. Besides, a solid line shows an assumed movement amount when the charging does not occur, a broken line shows a movement amount when the charging occurs.
Referring to FIG. 12, the graph showing the movement amount of the electrode when the charging occurs has been shifted to a high voltage side than the graph showing the assumed movement amount of the electrode when the charging dose not occur. Besides, the movement amount when the charging occurs decreases drastically than the assumed movement amount when the charging does not occur, in spite of drive voltage being applied same.
A difference between the drive voltage needed when the charging occurs and the drive voltage needed when the charging dose not occur, is called a charging voltage for moving the upper electrode by the predetermined movement amount. FIG. 12 is showing an example of the charging voltage.
FIG. 13 is a graph showing a change of light amounts of diffraction light generated by the GLV element by the charging phenomenon as described above in the GLV element composed of the electrostatic machine element 100. In FIG. 13, the x-axis shows a relative value of a drive voltage and the y-axis shows a relative value of a diffraction light amount. Besides, a solid line shows an assumed diffraction light amount when the charging dose not occur, a broken line shows a diffraction light amount when the charging occur.
Referring to FIG. 13, although the graph showing the assumed diffraction light amount when the charging dose not occur, shows symmetrical with a straight line showing a drive voltage zero. However, the graph showing the diffraction light when the charging occurs shows right shift against a straight line showing a drive voltage zero. Besides, the diffraction light amount when the charging occurs decreases drastically than the assumed diffraction light amount when the charging dose not occur, in spite of being drive voltage applied the same.
As illustrated in FIG. 12, for obtaining the diffraction light of the predetermined amount, a difference between the drive voltage needed when the charging occurs and the drive voltage needed when the charging dose not occur is called a charging voltage for moving the upper electrode to the predetermined diffraction light amount. FIG. 13 is showing an example of the charging voltage.
As a method for solving this problem, it is known a method in which a polarity of the drive voltage is reversed alternately in a short period to ease this phenomenon (U.S. Pat. No. 6,144,481) for example. However, because the voltage applied alternately with the device changes with a time series, for example, even if the polarity of the drive voltage is changed alternately, actual devices are not able to neutralize entirely the influence. Therefore, electric charges accumulated between the upper electrode and the lower electrode increase cumulatively with heterogeneous to cause a phenomenon able to not influence a predetermined electrostatic force at the upper electrode and the lower electrode after a long drive time.
Besides, although it is considered a method in which for example the dielectric films 103 and 104 between the upper electrode and the lower electrode are removed as a method for neutralizing an accumulating electric charge, these methods have practical problems for an influence on reliability of an element, for example.
Besides, although it is considered a method for lacking electric charges in the upper electrode and the lower electrode, it is practically difficult to be lacked in movement electric charge species like migratory ions until a practical using level.
The present invention is made in consideration of the above situation and the present invention has a first object to provide an electrostatic machine element able to restrain deterioration of practical electrostatic force between electrodes by the electrostatic shielded effect to prevent instability of an electrode movement.
Besides, the present invention has a second object to provide a light diffraction modulation element using the electrostatic machine element as described above.
Besides, the present invention has a third object to provide an image display device using the light diffraction modulation element as described above.
To achieve the above objects, the electrostatic machine element of the present invention includes a displaceable or deformable first electrode, a second electrode oppositely arranged to the first electrode, a first dielectric film formed at one side of the first electrode opposed to the second electrode and a second dielectric film formed at one side of the second electrode opposed to the first electrode, said first electrode being displaced or deformed in a direction perpendicular to the second electrode when a voltage between the first and second electrodes is applied and the second dielectric film including dielectric material of which a mobility showing a degree of movement of an electric charge depends on a polarity of the electric charge, the electric charge existing at a surface of the second dielectric film, being aparted from there and moved by an electric field between the first and second electrodes.
According to the electrostatic machine element of the present invention, the second dielectric film is formed by dielectric material by which a mobility of the electric charge existing at the surface of the second dielectric film depends on the polarity of the electric charge when the voltage is applied between the first and the second electrodes, so that the electric charge of the second dielectric film surface is movable comparatively easily to the first dielectric film by the electric field between electrodes.
Besides, to achieve the above objects, the light diffraction modulation element of the present invention includes a common electrode, a plurality of first electrodes oppositely arranged to the common electrode, a common dielectric film formed at one side of the first electrode opposed to the common electrode and a first dielectric film formed at one side of the first electrodes opposed to the common electrode, one of the adjoining first electrodes being displaced or deformed in a direction perpendicular to the common electrode when a voltage between one of the adjoining first electrodes and the common electrodes is applied, not making an incident light striked another side of a plurality of first electrodes an odd degree diffraction light at a first status, and making an odd degree diffraction light according to a difference in a level at a second state and the common dielectric film including dielectric material of which mobility showing a degree of movement of an electric charge depends on a polarity of the electric charge, the electric charge existing at a surface of the common dielectric film, being aparted from there and moved by an electric field between the first electrode and the common electrode.
According to the light diffraction modulation element of the present invention, the second dielectric film is formed by dielectric material by which a movement degree of the electric charge for existing at the surface of the second dielectric film depends on a polarity of the electric charge when the voltage is applied between the one adjoining first electrode and the common electrode, so that the electric charge of the second dielectric film surface is movable comparatively easily to the first dielectric film by the electric field between electrodes.
Besides, to achieve the above objects, the image display device irradiates a light diffraction modulation element with irradiation light from a light source to display an emitted light from the light diffraction modulation element at a display means to thereby form image, and the light diffraction modulation element includes a common electrode, a plurality of first electrodes oppositely arranged to the common electrode, a common dielectric film formed at one side of the first electrode opposed to the common electrode and a first dielectric film formed at one side of the common electrode opposed to said first electrode, one of the adjoining first electrodes being displaced or deformed in a direction perpendicular to the common electrode when a voltage between one of adjoining the first electrodes and the common electrode is applied, not making an incident light striked another side of a plurality of the first electrodes an odd degree diffraction light at a first status, and making an odd degree diffraction light according to a difference in a level at a second status, and the common dielectric film including dielectric material of which a mobility showing a degree of movement of an electric charge depends on a polarity of the electric charge, the electric charge existing at the surface of the common dielectric film, being aparted from there and moved by an electric field between the first electrode and the common electrode depends on a polarity of the electric charge.
According to the image display device of the present invention, the second dielectric film is formed by dielectric material by which a mobility of the electric charge existing at the surface of the second dielectric film depends on a polarity of the electric charge when the voltage is applied between the one of adjoining first electrode and the common electrode, so that the electric charge of the second dielectric film surface is movable comparatively easily to the first dielectric film by the electric field between electrodes.